[Pw_forum] Pw_forum Digest, Vol 51, Issue 44

[kondaiah samudrala]

Dear Sir,

  Thank you for your reply. I am sorry for not sending complete details.
Here i am running Black phosphorous, which is layered compound and reported
that havng huge van der waals forces. Genarally systems having van der waals
forces shows volume change( either 10-12% underestimate in LDA or 5-6%
overestimate in GGA)  with experimental volume in DFT calculations. In my
case,CASTEP and VASP i got similar variation in volume. But in PwSCF, i got
2% volume change with experimental volume. Here i used 50Ry cutoff and
10X10X10 K-mesh is used for my calculations. For energy minimum i used upto
10e-8 .Where as in "vc-relax" calculations i got 10% volume change with
experimental volume.

 please give your suggestions for my problem. If it is need i will send my
b/a, c/a and a calculation input  and output files to your mail.

with regards
S.Appalakondaiah
Research scholar
University of Hyderabad
Hyderabad
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